1. Field of the Invention
One embodiment of the present invention relates to a test method of a semiconductor device.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a power storage device, an imaging device, a memory device, a processor, an electronic device, a method for driving any of them, a method for manufacturing any of them, a method for testing any of them, and a system including any of them.
2. Description of the Related Art
In the case where a two-transistor and one capacitor gain-cell memory device, a three-transistor and one capacitor gain-cell memory device, or a memory device using a dynamic random access memory (DRAM) is used as a non-volatile memory, a writing transistor needs to have an extremely low off-state current. The off-state current affects the retention time because a change from 1×10−23 A to 1×10−22 A increases the leakage current tenfold, even though the value is in the range of an extremely low off-state current. However, a change in the extremely low off-state current cannot be measured with the retention time unless the measurement time is as long as one year or ten years.
To verify that the off-state current is extremely low, the off-state current can be estimated from the threshold voltage of a writing transistor and the slope of the current-voltage curve in the subthreshold region (also referred to as a subthreshold swing value or an S value and defined as the amount of decrease in gate potential that is needed for a drain current to be reduced by one digit). Patent Document 1 discloses a method of determining the threshold voltage of a writing transistor in a memory device module.